PURPOSE: To simplify the constitution by eliminating the necessity of an all-power detecting circuit, by providing a circuit that finds an absolute value for an allotted time in front of a discrete Fourier transforming circuit.
CONSTITUTION: A digital input signal is applied to discrete Fourier transforming circuit 2 by way of input circuit 1 and absolute-value circuit 11. This transforming circuit 2, when absolute value circuit 11 permits the input signal to pass through it as it is, detects levels of different frequency components of input signals. At this time, when absolute value circuit 11 extracts an absolute value at allotted time, the value is integrated for a certain time and the square of the value is detected. So that the square output of the integral value can be compared with the input signal component in terms of time, comparing circuit 13 delays one and then uses the all approximate voltage of input signals as a threshold level to decide the existence of input signals over a range of many frequencies by comparing them.
IMAGAWA HITOSHI
SHIRAISHI YOSHIKATSU
MURAMATSU RIYUUJIROU
SHIMOE TOSHIO
NIPPON TELEGRAPH & TELEPHONE
OKI ELECTRIC IND CO LTD
HITACHI LTD
FUJITSU LTD